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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  131 


HABITS  AND   BEHAVIOR  OF  THE 

CORN-FIELD  ANT,   LASIUS 

NIGER  AMERICANUS 


BY  STEPHEN  A.  FORBES 
STATE  ENTOMOLOGIST 


URBANA,   ILLINOIS,   DECEMBER,   1908 


CONTENTS  OF  BULLETIN  No.  131 

PAGE 

Introductory f. 31 

Contents  oi  the  Nests 31 

Beginning  oi  a  New  Colony 32 

Size  oi  Colonies . : 34 

Intercolonial  Hostilities 35 

Area  occupied  by  a  Single  Colony 37 

Relations  to  other  Species  oi  Ants 38 

Behavior  within  the  Nest 38 

Adaptation  oi  Behavior  to  changing  Conditions 40 

An  Injury  to  Corn  by  Ants 41 

Effect  oi  a  Change  oi  Crop 42 


30 


HABITS  AND  BEHAVIOR  OF  THE  CORN- 
FIELD ANT,  LASIUS  NIGER 
AMERICANUS 

BY  STEPHEN  A.  FORBES,  STATE  ENTOMOLOGIST 

The  little  brown  ant  notorious  for  its  injuries  to  corn,  and  called 
by  us,  consequently,  the  corn-field  ant,  is  not  by  any  means  limited  to 
corn  fields,  but  is  abundant  in  all  cultivated  lands,  in  pastures  and 
meadows,  in  dense  forests,  along  hard  pathways,  and  in  the  sandy  soil 
of  dry  sunny  roads.  One  sometimes  finds  it  nesting  in  rotten  wood 
or  under  bark,  logs,  or  stones,  and  even  opening  up  its  underground 
burrows  to  the  surface  between  the  bricks  of  sidewalks  and  pavements. 
It  is  distributed  "over  the  whole  of  North  America,  except  the  extreme 
southern  and  southwestern  portions,  from  the  tree  line  on  the  highest 
mountains  to  the  sands  of  the  shore."*  Wheeler  says  that  it  is  the 
most  abundant  of  our  ants,  and  hence  of  all  our  insects. 

Its  homes  and  habits  have  been  chiefly  studied  in  corn  fields,  and 
there  it  forms  rather  extensive  settlements,  mainly  centered  in  the  hills 
of  corn,  several  adjacent  hills  so  occupied  by  it  being  connected  by  un- 
derground channels  by  way  of  which  members  of  the  same  family  may 
pass  from  hill  to  hill.  This  is  partly,  no  doubt,  because  in  corn  fields  it 
is  usually  in  possession  of  plant-lice  which  live  on  the  roots  of  corn  and 
which  contribute  to  the  support  of  the  ants  the  fluid  surplus  of  their 
own  food,  but  partly  also  because  in  the  corn  hills  it  is  undisturbed  by 
the  cultivator,  which  is  likely  to  tear  up  its  nests  if  they  are  established 
between  the  rows. 

CONTENTS  OF  THE  NESTS 

In  the  burrows  of  this  ant  one  may  find  a  rather  mixed  and  varied 
population,  consisting  of  the  eggs,  larvae,  pupae,  males,  females,  and 
workers  of  the  ants  -themselves,  together  with  the  various  species  of 
root-lice  harbored  by  them  and  certain  kinds  of  mites  which  share  its 
underground  habitations  on  terms  of  mutual  toleration  if  not  of  active 
friendship.  In  clover  fields  it  is  very  likely  to  have  in  its  nests  many 
mealy-bugs  (Pseudococcus  trifolii  Forbes)  of  a  species  which  infests 
the  roots  of  the  clover  plant,  and  these  it  treats  as  it  does  the  root-lice 
of  the  corn  plant,  seizing  them  and  carrying  them  away  when  its  nest 
is  disturbed,  just  as  it  hurries  out  of  sight  its  own  maggotlike  larvae, 
its  egglike  pupae,  and  its  minute,  spherical  white  eggs. 

The  contents  of  the  nest  are  not  precisely  the  same  at  all  times  of 
the  year.  In  winter,  for  example,  one  finds  in  it  no  males  or  pupae  of 
the  ants,  as  a  rule,  but  only  workers  and  larvae,  companion  mites,  and 
the  eggs  of  root-lice.  In  some  of  the  large  winter  nests  one -or  more 
wingless  queens  or  mother  ants  may  be  found,  altho  we  have  not  been 

*An  Annotated  List  of  the  Ants  of  New  Jersey,   by  Wm.   Morton   Wheeler.     Bull.   Am. 
Mus.  Nat.  Hist.,  Vol.  I.,  p.   393. 

31 


32  BULLETIN  No.  131  [December, 

able  to  satisfy  ourselves  that  this  is  true  of  all,  or  even  of  most,  of  the 
winter  communities  of  this  species.  A  careful  search  and  exploration 
of  all  the  tunnels  and  chambers  of  large  nests  have  often  failed  to  bring 
to  light  a  single  queen.  -Sometimes,  however,  two  or  more  queens  may 
be  seen  living  contentedly  in  the  same  worker  family,  performing  their 
proper  function  of  laying  eggs  for  the  increase  of  the  colony.  Besides 
these  large  composite  and  evidently  well-established  communities,  one 
may  often  find  single  females  in  the  ground,  sometimes  wholly  alone, 
and  sometimes  with  a  few  of  their  own  eggs,  a  few  larvae,  and  a  small 
number  of  workers  which  are  mainly  undersized,  but  with  no  root-lice 
in  possession  and  no  companion  mites.  Late  in  fall  these  scattered 
solitary  females  may  have  nothing  with  them  in  their  pocketlike  under- 
ground cells  except  a  small  cluster  of  their  own  eggs.  These  minor 
groups  with  a  single  female  in  charge,  are  the  beginnings  of  a  new 
family,  and  do  not  often  reach  more  than  a  score  or  so  of  individuals 
by  the  end  of  the  first  year.  The  larger  compound  groups  are  older 
families,  how  old  in  any  given  case  we  have  no  present  means  of 
knowing. 

BEGINNING  OF  A  NEW  COLONY 

Beginning  now  with  a  single  female,  which  came  out  from  an 
established  colony  as  a  winged  ant  but  later  broke  off  her  own  wings, 
burrowed  in  the  earth,  and  began  to  lay  eggs  for  another  generation, 
we  will  follow  the  history  of  the  new  enterprise  thru  the  first  year, 
so  far  as  our  notes  and  observations  enable  us  to  go.  Females  and 
males  hatching  from  pupae  as  winged  ants  in  the  underground  nests 
from  June  to  October,  swarm  out  of  their  burrows  as  if  by  common 
consent  in  August  or  September.  Such  an  occurrence  was  noticed  by 
Mr.  H.  Carman,  at  Urbana,  at  5  p.  m.  September  14,  1885.  Males 
and  females  came  rapidly  up  from  their  burrows  under  ground  and, 
climbing  the  nearest  blades  of  grass,  took  flight  one  by  one,  in  various 
directions,  the  workers  in  the  meantime  running  rapidly  about  in  a 
state  of  great  excitement.  The  males  perish  before  winter,  and  the 
scattered  females  go  into  the  ground,  each  making  for  herself  an  oval 
or  spherical  cavity,  the  beginning  of  a  new  family  home.  Some  of 
these  buried  females  begin  to  lay  eggs  in  summer  and  fall — August  15 
to  November  10,  as  we  have  seen  them — but  others  live  there  alone 
until  spring,  depositing  their  first  eggs,  according  to  our  observations, 
from  the  first  to  the  middle  of  May,  and  continuing  to  lay  additional 
eggs,  a  few  at  a  time,  until  September.  The  minute,  maggotlike,  foot- 
less, and  helpless  larvae  begin  to  hatch  from  these  eggs  in  June,  and 
this  hatching  process  may  continue  until  October.  The  first  larvae  to 
appear  are  fed  by  the  female  from  the  contents  of  her  own  stomach, 
which,  as  she  is  said  to  take  no  food  during  this  period,  are  believed  to 
come  from  the  nutriment  stored  up  in  her  own  body.*  We  have  found 

*Charles  Janet  has  lately  shown  that  the  muscles  of  the  wings  of  the  female,  used  only 
for  a  few  hours  during  her  whole  life,  break  down  within  her  body  into  a  food  supply  avail- 
able for  the  production  of  her  eggs  and  the  nourishment  of  her  young.  Anatomic  du  Corse- 
let et  Histolyse  des  Muscles  Vibrateurs,  apres  le  Vol  Nuptial  chez  la  Reine  de  la  Fourmi 
Lnsius  rtiger.  Limoges,  1908. 


1908]  THE  CORN-FIKLD  ANT  33 

the  oldest  larvae  full  grown  and  beginning  to  pupate  from  the  12th  to 
the  16th  of  June,  and  pupation  continues,  of  course,  thruout  the 
season,  as  larvae  from  the  later  eggs  successively  get  their  growth. 
The  first  workers  to  emerge  from  the  pupae  in  these  small  colonies 
come  out  early  in  July — from  the  7th  to  the  llth  of  that  month, 
according  to  our  experience — and  the  last  emerge  in  October,  or  pos- 
sibly in  November. 

From  solitary  queens  brought  in  from  the  field  April  26  to  May  3, 
1906,  and  kept  in  the  insectary  under  natural  conditions,  the  first  eggs 
were  obtained  May  8,  9,  10,  and  15,  and  the  first  larvae  from  these  eggs 
June  4.  The  length  of  the  egg  stage  in  the  various  lots  deposited  by 
these  females  varied  from  twenty-two  to  twenty-eight  days.  The  larvae 
began  to  pupate  about  the  middle  of  June,  the  larval  period  being,  in 
four  cases,  sixteen,  seventeen,  nineteen,  and  twenty-three  days.  The 
first  adult  appeared  in  this  cage  July  7,  and  others  emerged  at  intervals 
thruout  the  remainder  of  the  year,  the  pupal  stage  averaging  about 
eighteen  days.  Judging  by  these  data,  the  time  from  the  deposit  of 
the  egg  to  the  appearance  of  the  adult  is  approximately  two  months. 
In  several  cases  where  second  egg-masses  were  laid  on  dates  definitely 
ascertained,  these  dates  were  found  to  coincide  closely  with  the  time 
of  pupation  of  larvae  from  the  previous  lot  of  eggs  laid  by  the  same 
-female. 

The  notes  of  my  field  observers  make  no  definite  statements  as  to 
the  numbers  thus  produced  during  the  first  season  of  the  queen's  inde- 
pendent life,  but  three  families  reared  under  observation  in  our  insec- 
tary, in  1906,  gave  respectively,  8, 9,  and  19  workers  as  the  final  product 
of  the  season's  operations.  These  numbers  are  perhaps  too  small  for 
the  average  in  the  field,  altho  larger  than  those  of  families  reared  dur- 
ing the  first  year  by  the  carpenter-ant,  as  reported  by  Pricer  in  1907.* 
Forty-one  first-year  colonies  of  this  latter  species  contained  from  2  to 
27  workers,  with  an  average  of  10;  and  19  colonies  of  a  related  ant 
(Camponotus  ferrugineus")  contained  from  2  to  19  workers,  with  an 
average  of  only  6. 

The  process  of  growth  and  multiplication  are  interrupted  by 
winter,  during  which  the  ants  hibernate  in  a  dormant  state  in  whatever 
stage  they  happen  to  have  reached,  resuming  their  activities  in  spring 
at  the  point  where  cold  weather  arrested  them.  The  workers  open  up 
the  nests  to  the  surface,  usually  in  late  March  or  in  April,  the  evidence 
of  this  beginning  of  their  seasonal  activities  being  the  appearance  of 
circular  heaps  of  minute  pellets  of  earth  around  the  mouths  of  their 
burrows.  The  young  larvae  grow  little,  if  at  all,  as  long  as  the  weather 
is  cool,  but,  fed  and  cared  for  by  the  workers,  increase  rapidly  in  size 
as  soon  as  the  weather  becomes  warm,  the  oldest  of  them  reaching  the 
pupal  state  as  early  as  May.  Whether  males  and  females  appear  in  the 
family  colony  during  this  second  summer  is  not  definitely  known,  but 
it  is  rendered  very  doubtful  by  the  small  size  of  the  family  during  the 

•The  Life  History  of  the  Carpenter-ant,  by  John  Lessen  Pricer.     Biological  Bulletin,  Feb- 
ruary, 1908,  pp.  177-218. 


34 


BULLETIN  No.  131 


[December, 


first  spring  and  by  Pricer's  observations  concerning  the  carpenter-ant, 
from  which  he  concludes  that  winged  males  and  females  do  not  appear 
in  the  colony  until  it  is  more  than  two  years  old.  Some  support  for 
this  conclusion  as  applying  to  our  corn-field  ant  will  presently  be  given. 
We  can  not  follow  the  history  of  the  colony  farther  at  this  time,  lack- 
ing detailed  knowledge  of  the  rate  of  its  increase  and  the  form  of  its 
organization.  We  only  know  that  family  groups  enlarge  to  contain 
several  hundred  workers,  and  larvae  sometimes  by  the  thousand,  with 
pupae,  males,  and  queens  in  much  smaller  numbers. 

SIZE  OF  COLONIES 

The  following  table  shows  the  number  of  ants  of  all  stages  con- 
tained in  20  nests  dug  out  in  an  oats  field  by  Mr.  Kelly  August  28, 
1906.  The  fact  that  the  larger  numbers  are  all  multiples  of  10  or  5 
shows  that  these  counts  are  not  to  be  regarded  as  exact. 

ANTS  IN  TWENTY  NESTS,  IN  OATS  FIELD,  AUGUST  28,  1906 


Workers 

- 
> 

ft! 
a 

a 

da 

•  "rt 

Young 

females 

H 
U 

a 

1 

41 

60 

16 

0 

'  0 

1 

0 

118 

75 

50 

16 

0 

0 

1 

0 

142 

160 

400 

30 

0 

0 

590 

183 

435 

15 

5 

17 

655 

190 

530 

60 

26 

4 

810 

220 

430 

75 

21 

3 

1 

7 

757 

260 

650 

210 

11 

27 

1158 

280 

340 

120 

12 

20 

772 

330 

150 

240 

6 

24 

750 

340 

150 

60 

0 

5 

555 

360 

750      30 

13 

33 

1186 

380 

420      35 

A 

19 

856 

410 

700 

120 

14 

21 

1265 

475      235 

115 

0 

16 

841 

540 

150 

250 

6 

29 

975 

585 

280 

125 

0 

16 

• 

1006 

680 

240 

125 

31 

12 

1088 

740 

310      180 

19 

15 

1264 

sea 

200 

160 

16 

34 

1270 

900 

450 

25 

21 

38 

1434 

It  will  be  noticed,  on  examining  this  table — the  figures  for  which 
are  arranged  in  the  order  of  the  number  of  workers  in  each  nest — that 
the  first  three  colonies  are  of  a  different  class  from  the  remainder, 
marked  by  the  absence  of  winged  ants  of  either  sex,  and  by  relatively 
small  numbers  of  worker  larvae  and  worker  pupae.  These  numbers  are 
apparently  too  large,  however,  for  a  first-year  colony,  and  are  probably 
the  result  of  two  years'  multiplication  from  the  sole  queen  founder. 
Possibly  the  third  of  the  series,  with  its  160  workers,  400  larvae,  and 
30  pupae,  is  a  third-year  family.  The  small  number  of  males  and 


1908]  THE  CORN-FIELD  ANT  35 

females  in  the  remaining  families  as  compared  with  the  workers,  larvae, 
and  pupae,  can  not  be  explained  without  a  better  knowledge  of  the 
economy  of  this  species.  It  will  be  noticed  that  the  fully  developed 
nests,  that  is,  those  containing  ants  in  the  various  stages  due  at  this 
season  of  the  year,  vary  in  number  from  655  to  1434,  with  an  average 
for  the  17  larger  nests  of  979. 

It  is  probable  that  families  reach  their  largest  size  in  grass-lands, 
where  they  may  multiply  without  disturbance  year  after  year;  and 
consistently  with  this  supposition  Mr.  Kelly  found  in  following  the 
plow  in  a  field  of  grass  in  April,  1906,  some  of  the  largest  nests  of 
our  record.  In  one  nest  were  nearly  6000  larvae  and  300  workers, 
with  no  eggs,  no  pupae,  and  no  queen.  Thirty-nine  other  nests  in  this 
field  were  seemingly  as  large  as  this. 

INTERCOLONIAL  HOSTILITIES 

The  well-known  but  remarkable  hostility  of  ants  of  one  colony  to 
those  of  another  of  their  own  species  is  well  illustrated  by  many  of  the 
observations  of  my  field  and  laboratory  assistants. 

For  example,  the  first  of  April,  1906,  a  strange  queen  introduced 
to  a  group  of  some  forty  workers  of  the  corn-field  ant  confined  in  a 
formicary,  was  ruthlessly  attacked  and  killed  by  them  as  an  intruder. 
Precisely  the  same  observation  was  made  in  another  case  April  27. 

August  15,  1905,  a  wandering  lone  queen  placed  in  a  formicary 
inclosure  with  five  males  from  another  locality  killed  two  of  them 
the  same  day.  During  the  following  night  two  stray  worker  ants  of 
her  species  entered  the  formicary  thru  a  crevice  and  attacked  the 
queen,  one  of  them  seizing  her  foot  with  its  mandibles  and  holding 
fast  for  an  hour  and  a  half,  when,  as  it  could  not  be  compelled  to 
release  the  queen,  it  was  killed  to  save  her. 

August  t6,  1905,  a  strange  male  was  first  placed  among  twenty 
workers  in  a  formicary,  but  being  instantly  attacked  it  was  transferred 
to  another  containing  only  a  lone  queen — one  who  having  rid  herself 
of  her  wings  was  presumably  already  fertilized.  The  male  being  dead 
in  the  morning,  the  presumption  is  strong  that  the  queen  killed  if.  In 
another  case,  occurring  August  15,  four  males  placed  in  the  nest  with 
a  strange  queen  were  immediately  attacked  by  her,  and  two  of  them 
were  presently  killed.  On  the  other  hand,  a  queen  ant  still  bearing  her 
wings,  placed  alone  with  a  strange  male  August  21,  made  friends 
with  him  immediately.  The  two  continued  to  live  in  harmony,  the 
queen  sometimes  caressing  the  male  and  even  apparently  feeding  him, 
until  the  26th,  when  she  began  to  try  to  pull  off  her  wings  and  refused 
to  have  anything  further  to  do  with  the  male.  September  6,  altho  still 
bearing  her  wings,  having  failed  in  her  efforts  to  remove  them,  she 
began  to  lay  -eggs.  This  seems  a  possible  case  of  fertilization  of  the 
queen  within  the  formicary,  but  direct  observations  to  that  effect  are 
wanting. 

August  16,  a  male  from  one  formicary  put  in  with  the  workers  of 
another  was  immediately  pounced  upon  by  them,  and  would  evidently 
have  been  killed  if  he  had  not  been  promptly  rescued. 


36  BULLETIN  No.  131  [December, 

August  15,  worker  ants  taken  from  two  different  nests  in  the  field 
and  placed  in  the  same  formicary  began  at  once  'to  fight.  They  kept 
up  their  contest  all  night,  and  several  of  them  were  dead  in  the  morn- 
ing. By  noon  of  the  following  day,  however,  fighting  had  ceased 
and  the  two  groups  had  separated,  occupying  different  parts  of  the' 
enclosure.  The  larger  group  had  taken  possession  of  a  corn  plant 
which  had  been  introduced  for  the  use  of  these  ants,  and  the  other 
colony,  which  established  itself  near  the  edge  of  the  formicary,  seemed 
timid  and  cowed,  apparently  fearing  even  to  feed  upon  the  syrup 
offered  them.  The  dominant  group  mined  actively  in  the  earth  about 
the  roots  of  the  corn,  and  appropriated  the  root-lice  introduced  into 
the  cage,  evidently  feeling  themselves  masters  of  their  domain. 

April  24,  1906,  a  colony  of  100  worker  ants  with  200  larvae  of 
various  sizes,  and  eggs  of  the  corn  root-aphis,  were  brought  in  from 
the  field  and  established  in  a  two-celled  glass  formicary.  After  they 
had  become  thoroly  at  home,  nine  worker  ants  and  a  few  ant  larvae — 
strangers  to  the  original  colony — a  bunch  of  aphis  eggs,  and  some 
young  root-aphids,  were  introduced  into  this  nest,  the  original  family 
being  in  the  orange  or  dark  cell  and  the  newcomers  in  the  other  cell 
of  this  cage.  As  soon  as  the  presence  of  the  strangers  was  detected 
they  were  attacked  by  the  old  colony,  which  dragged  the  adults  about, 
killing  them  one  by  one,  ate  up  their  larvae,  ate  or  pulled  to  pieces  the 
root-lice  introduced  with  them,  and  crushed  the  aphis  eggs.  The  root- 
lice  and  eggs  brought  in  from  their  own  nest  they  were  in  the  mean- 
time caring  for  as  usual. 

August  7,  some  eggs  of  the  corn-field  ant  brought  in  from  the 
field  and  placed  with  a  colony  of  workers  well  established  in  an  artifi- 
cial formicary,  were  presently  found  by  one  of  the  workers  and  delib- 
erately crushed,  one  by  one. 

These  hostilities  of  ants  to  strangers  may  extend  even  to  those 
of  their  own  sisterhood  who  have  been  away  from  home  too  long. 
For  example,  a  young  worker  separated  from  its  formicary  mates 
August  21,  kept  alone,  and  returned  to  them  twenty-one  days  later, 
was  immediately  attacked  by  them  and  quickly  killed. 

The  utility  to  the  ants  of  this  inhospitable  savagery — this  spirit  of 
ferocious  clannishness — is  doubtless  to  be  found  in  their  social  organ- 
ization, and  in  the  necessity  under  which  they  live  of  keeping  always 
an  active,  compact,  deeply  interested  group  of  workers  completely 
devoted  to  the  care  and  nurture  of  their  helpless  young.  No  young 
of  any  animal  can  be  more  utterly  dependent  than  those  of  these  ants, 
and  their  feeding  and  protection  must  be  the  constant,  consuming  care 
of  the  whole  family  group. 

The  workers  are,  on  the  other  hand,  among  the  most  active  and 
enterprising  wanderers  and  foragers  among  insects,  traveling  far  and 
wide  on  foot  to  distances  which  make  it  necessary  for  them  to  retrace 
their  steps  carefully,  whether  by  the  aid  of  the  sense  of  sight  or  by 
antennal  senses  supposed  to  resemble  what  in  us  is  the  sense  of  smell. 
The  homing  instinct  and  the  nursing  instinct  are  in  them  so  strong  as 


1908]  THE  CORN-FIELD  ANT  37 

practically  to  rule  their  lives.  They  go  abroad  in  search  of  food  for 
the  family,  and  to  the  family  they  must  return,  however  far  they  may 
travel  and  into  whatever  difficulties  and  adventures  they  may  fall  by 
the  way. 

These  facts  make  it  necessary  that  there  should  be  in  the  economy 
of  ant  society  some  self-acting,  self-regulating  apparatus  for  keeping 
the  family  groups  wholly  separate  and  distinct,  for  making  sure  that 
every  foraging  worker  shall  find  its  way  back  to  its  own  companions 
— that  it  shall  neither  be  liable  to  lose  its  way  completely  nor  likely  to 
attach  itself  to  an  alien  family.  From  this  point  of  view  it  is  greatly 
to  the  general  interest  that  it  should  find  a  welcome  and  a  permanent 
home  only  among  its  immediate  kindred  and  habitual  companions,  and 
nothing  could  make  this  condition  more  secure  than  a  universally 
hostile  reception  to  the  wanderer  in  every  other  family  group.  Clan- 
nishness  in  ants  has  thus  the  same  justification  that  it  has  among 
savage  men.  It  is  a  means  of  maintaining  the  necessary  concentration 
of  the  group  for  the  care  of  the  young,  and  hence  for  the  preservation 
of  the  race. 

AREA  OCCUPIED  BY  A  SINGLE  COLONY 

Practical  advantage  was  taken  by  us  of  this  intolerance  of  ants 
towards  those  of  other  parentage  to  ascertain  the  limits  in  the  corn- 
field of  a  single  colony  or  family  group.  Assuming  that  specimens 
from  adjacent  hills  of  corn  are  members  of  the  same  family  if  they 
affiliate  peaceably,  but  that  they  belong  to  different  families  if  they 
fight,  I  instructed  my  field  assistant  to  bring  the  inhabitants  of  adja- 
cent hills  into  contact  with  each  other  in  artificial  nests  until  all  those 
affiliating  with  the  original  group  used  as  a  test  were  distinguished 
from  those  about  them  who  refused  peaceable  affiliation.  By  a  care- 
ful application  of  this  method  at  Elliott,  May  23,  1906,  two  family 
areas  were  thus  marked  out. 

The  group  of  hills  included  in  the  first  experiment  occupied  an 
area  10  hills  in  length  by  7  in  width,  and  20  of  these  70  hills  were  in- 
fested by  ants.  Selecting  the  inhabitants  of  a  hill  from  the  center  of 
this  tract  for  the  purposes  of  this  test,  ants  from  the  other  infested 
hills  were  placed  with  them  successively.  By  this  means  it  was  found 
that  the  inhabitants  of  ten  of  these  hills  were  members  of  one  com- 
munity, harmonizing  with  each  other  perfectly  when  commingled,  but 
that  those  of  the  other  nine  were  strangers  to  them,  since  the  repre- 
sentatives of  these  groups  instantly  fought  when  placed  together.  The 
ten  nests  thus  identified  as  related  were  distributed  over  an  irregular 
area  about  30  feet  long  by  14  feet  in  greatest  width,  and  were  proba- 
bly all  connected  by  a  network  of  underground  channels.  Hills  inhab- 
ited by  hostile  ants  were  in  many  cases  immediately  next  to  others 
occupied  by  members  of  this  family  group. 

Trie  second  experiment  covered  a  plot  of  130  hills,  32  of  which 
were  occupied  by  the  corn-field  ant.  The  occupants  of  12  of  these 
hills  affiliated  peaceably,  while  the  remaining  20  were  rejected  by  the 


38  BULLETIN  No.  131  [December, 

original  colony  used  in  making  the  test.  The  family  settlement  thus 
outlined,  also  irregular  in  shape,  was  about  30  feet  long  by  10  feet  in 
greatest  breadth.  There  was  rio  intermingling  of  hostile  groups  in 
either  of  these  family  areas,  all  the  ants  occupying  hills  within  the 
boundaries  of  each  being  on  friendly  terms. 

RELATIONS  TO  OTHER  SPECIES  OF  ANTS 

Notwithstanding  the  almost  invariable  intolerance  exhibited  by 
different  families  of  the  corn-field  ant  towards  each  other,  they  some- 
times live  on  perfectly  friendly  terms  with  ants  of  other  species,  both 
kinds  mingling  harmoniously  in  the  same  galleries  among  the  roots  of 
the  same  rrlls  of  corn.  One, of  the  small  red  house-ants  (Solenopsis 
molesta)  which  often  infests  kitchens  and  pantries  to  the  annoyance 
of  the  housekeeper,  is  frequently  found  at  home  in  the  nests  of  our 
corn-field  species.  A  mixed  settlement  of  these  two  ants  found  in  a 
field  near  Urbana  August  31,  1905,  and  brought  to  the  insectary  and 
established  in  a  jar  of  earth,  collected  their  larvae  and  pupae  into  sep- 
arate lots  without  contention,  and  continued  for  several  days  to  feed 
peaceably  together  from  the  same  food  supply.  August  29  another 
species  common  in  corn  fields,  Formica  schaufussi,  was  found  by  Mr. 
Kelly  inhabiting  the  nests  of  Lasius  niger  americanus,  the  larvae  and 
pupae  of  both  being,  as  he  says,  mingled  in  the  same  heap.  Trans- 
ferred to  a  Mason  fruit- jar  and  brought  to  the  insectary,  they  lived 
together  for  two  days  in  a  Lubbock  nest  without  fighting;  but  after- 
wards hostilities  broke  out  and  all  the  Formicas  were  killed  save  two 
which  remained  in  hiding,  and  their  pupae  were  thrown  by  their  con- 
querors into  the  ditch  surrounding  the  nest. 

BEHAVIOR  WITHIN  THE  NEST 

From  a  colony  of  ants  obtained  August  15  and  established  in  a 
Fielde  nest,  one  of  seven  queens  was  removed  and  placed  by  herself 
August  16  in  a  glass  Petrie  dish  with  moist  earth,  for  special  observa- 
tion. She  had  broken  off  her  wings  the  previous  day,  and  was  hence 
presumably  fertilized,  altho  she  apparently  had  not  left  her  native 
nest.  She  began  at  once  working  in  the  earth  as  if  to  make  a  burrow. 
This  is  the  queen  which  killed  a  male  placed  with  her,  as  described  on 
another  page.  She  worked  restlessly  in  the  earth  for  several  days, 
helping  herself  to  the  sugar  syrup  offered  her,  and  deposited  six  eggs 
August  25.  It  is  commonly  supposed  that  a  fertile  queen  does  not 
feed  after  leaving  the  family  nest  until  she  has  reared  workers  capable 
of  supplying  her  with  food.  Possibly  her  nest  was  kept  too  dry  and 
the  syrup  was  taken  as  drink  rather  than  as  food. 

Another  queen  brought  in  from  the  field  August  15,  pulled  off 
three  of  her  wings  within  the  next  two  days,  but  did  not  succeed  in 
ridding  herself  of  the  fourth  until  August  25.  This  queen  was  re- 
ported by  Mr.  Kelly  to  partake  once  or  twice  a  day  of  the  syrup  placed 
in  her  cell.  She  busied  herself  with  piling  up  the  dirt  beside  a  bit  of 
wet  sponge,  sometimes  undoing  at  one  time  what  she  had  done  at 
another.  She  laid  no  eggs,  and  died  September  6. 


1908]  THE  CORN-FIELD  ANT  39 

The  significance  of  males  in  the  ordinary  life  of  the  colony  is 
very  small,  and  I  have  but  few  notes  on  their  habits  and  behavior. 
July  31  a  worker,  a  male,  and  a  pupa  were  placed  together  in  a  Petrie 
dish,  the  pupa  almost  mature.  This  is  a  situation  of  great  responsi- 
bility for  the  worker  ants,  whose  aid  is  necessary  to  the  successful 
emergence  of  the  adult,  and  the  single  worker  upon  whom  these  labors 
fell  made  every  effort  to  discharge  her  duties  alone,  the  male  doing 
nothing  in  her  aid.  The  anxious  and  affectionate  worker  divided  her 
attentions  between  the  helpless  pupa  and  this  idle  male,  caressing  and 
feeding  him,  and  when,  thru  a  misadventure,  his  wings  were  stuck  to 
the  cover  of  the  cell  in  the  moisture  which  collected  there,  doing  her 
best  to  pull  him  loose.  When  the  pupa  was  ready  to  yield  the  adult 
the  end  of  the  pupa-case  was  bitten  off  by  the  worker  ant,  and  its  in- 
mate pulled  out  head  first  in  a  helpless  condition,  unable  even  to  stand. 
In  about  three  hours,  however,  it  was  walking  about. 

When  the  workers  were  moving  the  family  from  one  cell  of  the 
formicary  to  another,  they  were  often  seen  dragging  the  males  along 
to  the  new  quarters,  as  if  ants  of  this  stupid  sex  were  unable  to  get 
any  idea  of  what  was  going  on,  and  must  be  dealt  with  by  physical 
force. 

The  responsibility  of  the  workers  for  the  successful  transforma- 
tion of  the  pupa  and  the  appearance  of  the  adult  is  well  illustrated  by 
an  observation  recorded  by  Mr.  Kelly  under  date  of  August  17.  In  a 
glass  Petrie  dish  in  which  three  workers  and  three  pupae  of  the  corn- 
field ant  had  been  placed  for  observation  August  2,  a  worker  emerged 
from  a  pupa-case,  two  of  the  workers  in  the  cell  assisting.  One  of 
these  bit  off  the  black  tip  of  the  pupa-case  and  slowly  pulled  the  young 
ant  out,  taking  three  minutes  for  4he  operation.  The  head  of  the  new- 
born worker  was  cleaned  off v  and  its  antennas  were  straightened  o>ut 
by  the  mouth-parts  of  one  of  its  nurses,  while  the  other  loosened  and 
straightened  its  legs.  At  the  end  of  sixteen  minutes  from  its  release 
it  made  its  first  attempts  to  walk.  In  this,  as  in  other  cases  observed, 
the  workers  rewarded  themselves  by  devouring  the  empty  pupa-case. 

The  constant  attention  which  the  worker  ants  pay  to  their  eggs 
and  larvae  is  so  well  known  that  it  scarcely  requires  illustration.  Many 
of  their  ministrations,  it  is  true,  seem  aimless  and  mechanical,  mere 
restless  movements  of  their  charges  from  place  to  place,  but  the  con- 
stant attention  given  by  the  workers  to  their  young  is  an  effective  safe- 
guard against  any  ordinary  injury. 

The  .eggs,  deposited  by  the  female,  are  gathered  together  by  the 
workers,  kept  in  a  pile  or  ball  convenient  of  transportation  in  a  mass, 
and  carried  up  and  clown  in  the  nest  according  to  the  weather;  and  as 
they  hatch  the  young  are  separated  from  the  mass  of  eggs  and  kept 
by  themselves,  usually  assorted  according  to  size  as  they  increase  in 
number  and  differ  in  age.  Larvae  and  pupae  are  likewise  commonly 
kept  distinct,  the  various  lots  doubtless  requiring  somewhat  different 
care. 

The  workers  feed  their  larvae  almost  constantly  from  the  contents 
of  their  own  stomachs,  and  often  mouth  and  hover  them,  a  mass  of 


40  BULLETIN  No.  131  [December, 

the  ants  clustering  around  and  over  them  in  a  way  to  conceal  them 
from  view.  When  the  colony  is  established  in  a  two-celled  nest,  one 
covered  with  clear  glass  and  the  other  with  orange,  the  workers  con- 
vey their  young  to  the  orange  cell,  the  light  transmitted  by  orange 
glass  being,  as  shown  by  Miss  Fielde,  inappreciable  by  ants. 

Even  after  the  workers  have  emerged  from  the  pupa-case  they 
are  still  watched  and  cared  for  by  their  more  experienced  relatives, 
and  often  fed  in  the  nest  by  foragers  returning  from  outside.  This 
operation  was  illustrated  in  our  breeding-cages  when  pale  young 
workers  remaining  within  the  orange  cell  were  fed  by  the  darker, 
older  ones  from  food  exposed  to  them  in  the  light  cell  of  the  formicary. 

The  nursing  instinct  of  the  workers  is  so  overruling  that  it  ex- 
tends to  all  the  inmates  of  the  nest  excepting  only  strangers  of  their 
own  species.  A  common  resident  of  the  nest  of  these  ants  is  a  species 
of  mite  (Macrocheles  mastus  Banks)  often  found  crawling  about 
among  the  eggs  and  larvae,  altho  never  detected  in  any  depredation 
upon  them.  It  is  probably  a  scavenger  of  the  domicil,  and  is  thus 
possibly  entitled  to  the  protection  which  it  receives.  When  a  nest  con- 
taining these  mites  is  disturbed,  they  receive  the  same  attention  as  its 
other  inmates  from  the  alarmed  and  anxious  workers.  In  several 
nests  for  example,  plowed  up  April  24,  in  an  old  oats  field,,  mites  were 
commonly  present,  and  the  ants  seized  them  in  their  mandibles  and 
carried  them  away  as  they  did  their  own  young. 

ADAPTATION  OF  BEHAVIOR  TO  CHANGING  CONDITIONS 

The  movements  of  ants  in  their  outdoor  habitations  often  show 
a  surprising  adaptation  of  habit  and  behavior  to  changing  conditions 
in  the  field.  It  was  repeatedly  noticed,  for  example,  that  during  warm 
dry  weather  in  early  spring  the  aphis  eggs  would  often  be  brought 
near  the  surface  while  the  larvae  of  the  ants  were  kept  at  a  depth  of 
five  or  six  inches  below.  The  effect  of  this  treatment  must  be  to 
hasten  the  hatching  of  the  aphids  and  at  the  same  time  to  retard  the 
development  of  the  larvae  of  the  ants.  The  growth  of  the  latter  is  thus 
kept  practically  at  a  standstill  while  food  is  scarce  in  spring,  but  pro- 
ceeds at  a  rapid  pace  after  the  aphids  have  hatched  and  are  yielding 
an  abundant  food  supply  to  the  colony.  In  periods  of  summer  drouth 
the  burrows  are  extended  downward  to  a  depth  of  twelve  or  fifteen 
inches,  and  eggs,  larvae,  and  pupae  are  carried  down  into  relatively 
moist  earth.  The  ants  then  mass  up  in  the  depths  of  their  burrows 
and  are  rarely  seen  abroad,  but  communicate  with  their  root-louse 
herds  by  means  of  underground  passageways,  sometimes  several  feet 
in  length.  When  soaking  rains  come,  these  hidden  colonies  open  up 
their  burrows  to  the  surface  again,  as  the  ground  dries  off,  and  resume 
their  more  active  habits  as  general  foragers. 

Under  certain  conditions  of  serious  deprivation  and  suffering, 
however,  this  whole  system  breaks  down,  and  the  ants  may  devour,  for 
their  own  temporary  maintenance,  the  very  objects  to  which  they  have 
previously  devoted  their  entire  existence.  When  infested  plants  wither 


1908]  THE  CORN-FIELD  ANT  41 

and  die,  and  no  others  can  be  found  to  which  the  aphids  may  be  trans- 
ferred, these  are  themselves  eaten  by  the  workers  as  a  food  material 
too  valuable  to  waste.  When  suffering  from  a  lack  of  sufficient  animal 
food,  the  workers  in  our  formicaries  have  occasionally  helped  them- 
selves to  a  living  pupa  of  their  own  species,  or  have  even  devoured 
the  larvae  in  their  charge,  to  the  last  one.  The  corn-field  ant  is,  in  fact, 
essentially  a  carnivorous  insect,  and  forages  actively  for  animal  food, 
especially  when  it  is  without  a  sufficient  number  of  root-lice.  Much 
of  our  breeding-cage  work  came  to  naught  thru  the  mysterious  death 
of  the  workers,  apparently  because  their  liking  for  a  watery  syrup  was 
regarded  as  evidence  that  this  was  a  sufficient  food  for  them.  In  the 
field  and  in  the  insectary  we  have  seen  ants  feed  at  various  times  and 
under  various  conditions  upon  cutworms,  carabid  larvae,  white-grubs, 
dead  May-beetles,  dead  beetles  of  the  corn  root-worm,  dead  grasshop- 
pers, root-lice,  myriapods,  earthworms,  their  own  pupae  and  larvae,  and 
the  pupal  envelopes  vacated  by  adults  on  transformation.  Occasionally 
they  have  been  seen  injuring  corn  by  hollowing  out  the  soft  seed  either 
before  or  after  sprouting,  and  in  one  case  at  least  they  were  reported 
by  an  insectary  assistant  as  feeding  on  the  fibrous  roots  of  the  plant. 

AN  INJURY  TO  CORN  BY  ANTS 

Under  certain  conditions,  indeed,  this  corn-field  ant  may  do  con- 
siderable injury  to  corn  by  a  direct,  unaided  attack.  During  the*  cool, 
wet  spring  of  1905,  when  the  softened  kernels  lay  long  in  the  earth 
without  sprouting,  and  the  young  plants  grew  very  slowly  for  a  time, 
a  field  of  corn  following  oats,  heavily  infested  by  ants  which  had  no 
root-lice  in  their  possession,  was  considerably  damaged  by  the  ants, 
which  gnawed  and  hollowed  out  the  seed,  thus  either  killing  it,  or  so 
diminishing  the  food  reserve"  that  the  plant  made  a  slow  and  feeble 
start. 

This  field  of  forty  acres,  lying  near  Champaign,  had  been  in  oats 
in  1904,  in  corn  in  1903,  and  in  grass  in  1902.  The  corn  was  said  by 
the  tenant  to  have  been  injured  by  root-lice  in  1903,  the  part  worst 
infested  yielding  not  over  22  bushels  to  the  acre,  while  the  remainder 
of  the  field  gave  a  yield  of  55  to  60  bushels.  Owing  to  a  report  that 
the  young  corn  was  being  injured  by  ants,  Dr.  J.  W.  Folsom,  of  the 
University  department  of  instruction,  examined  it  for  me  May  31, 
digging  up  sixty-one  hills  in  a  way  to  expose  the  whole  root  system. 
Forty-one  of  these  hills  were  in  a  part  of  the  field  but  moderately  in- 
fested with  ants,  and  thirteen  were  in  an  adjacent  part  in  which  ants 
were  very  abundant.  In  both  cases  the  hills  examined  were  taken 
as  they  came,  one  after  the  other  in  the  row.  Seven  hills  additional 
were  dug  up  here  and  there,  because  of  an  especially  noticeable  infesta- 
tion. The  corn  in  this  field  was  unequal  in' condition,  the  poorer  hills 
being  most  numerous  where  ants  were  most  abundant.  This  unthrifty 
corn  was  four  or  five  inches  high,  and  of  a  yellowish  hue,  while  the 
better  plants  were  six  or  seven  inches  high,  and  of  a  good  green  color. 

In  the  less-infested  row  six  hills  out  of  forty-one  were  infested 
by  the  corn-field  ant,  one^  of  them  containing  also  the  red  house-ant 


42  BULLETIN  No.  131  [December, 

(Solenopsis  debilis).  In  five  of  the  six  infested  hills  a  single  kernel 
of  corn  had  been  more  or  less  eaten  by  the  ants.  No  observations  of 
injury  to  the  roots  were  reported,  but  the  amount  of  stunted  corn  in 
this  part  of  the  field  could  scarcely  be  accounted  for  except  on  the  sup- 
position that  some  other  injury  was  being  done  than  this  to  the  kernel 
in  the  hill.  In  the  worse-infested  part  of  the  field  thirteen  hills  were 
examined,  eleven  of  which  were  infested,  and  eight  of  them  contained 
kernels  which  had  been  more  or  less  eaten  by  the  ants.  In  five  of  the 
hills  all  the  kernels  had  been  thus  injured,  and  in  the  others  only  one 
kernel  to  the  hill.  The  ants  in  these  hills  were  all  the  common  corn- 
field species  except  in  one  instance,  where  only  Solenopsis  was  found. 
In  the  seven  hills  selected  because  of  their  visible  infestation,  all  the 
kernels  were  eaten  by  ants  in  two,  and  a  single  kernel  out  of  two  or 
three  in  each  of  the  others,  the  ants  in  all  these  hills  being  the  common 
corn-field  species.  Rough  estimates  of  the  number  of  ants  to  a  hill 
ranged  from  ten  workers  as  a  minimum  to  a  maximum  of  a  thousand. 
In  one  case  only  were  ant  larvae  present. 

In  all  these  sixty-one  hills  the  corn  root-aphis  was  found  but  four 
times — twice  a  single  winged  female,  once  a  winged  female  with  three 
large  and  thirty  small  wingless  females,  and  once  four  winged  females 
with  between  forty  and  fifty  wingless  ones,  nearly  all  of  them  young. 
There  were,  in  fact,  more  of  the  common  grass  root-louse  (Schisoneura 
panicola]  in  the  field  than  of  the  corn  root-aphis,  some  on  the  roots  of 
corn,  with  ants  in  charge,  and  others  on  smartweed  and  ragweed  roots, 
and  also  accompanied  by  ants. 

From  these  observations  we  may  infer  that  ants  living  in  the 
meadow-grass  in  1902  with  grass  root-lice  in  their  possession,  infested 
the  corn  the  following  year;  that  they  continued  in  the  field  through 
1904,  when  a  crop  of-  oats  was  raised,  carrying  a  small  percentage  of 
their  grass  root-lice  over  on  roots  of  weeds  in  the  field ;  and  that  when 
the  ground  was  planted  to  corn  in  1905  they  were  still  abundant  there, 
but  with  so  few  root-lice  in  their  possession  that  they  availed  them- 
selves of  the  softened  corn  kernels  in  the  earth  for  food,  probably 
gnawing  away,  also,  root  hairs  and  the  finer  roots,  as  they  have  been' 
seen  to  do  in  confinement. 

EFFECT  OF  A  CHANGE  OF  CROP 

The  effect  of  a  change  of  crop — from  corn  to  oats,  for  example — 
on  the  ant  population  of  a  badly  infested  field,  was  illustrated  by  an 
account  in  my  Thirteenth  Report  of  the  disappearance,  during  the 
latter  part  of  May,  of  both  ants  and  aphids  from  an  oats  field  formerly 
in  corn.  By  this  time  the  weeds  in  the  field  were  practically  all  dead, 
the  oats  having  reached  a  height  to  overshadow  and  sap  them.  A 
similar  occurrence,  more  closely  observed,  is  reported  by  Mr.  Kelly  in 
a  series  of  notes  running  from  April  21  to  June  22,  1906.  In  a  forty- 
acre  field  of  oats  fifty  nests  of  the  corn-field  ant  were  located  and 
marked  near  two  sides  of  the  field,  one  next  a  field  of  corn  and  the 
other  separated  from  corn  by  a  hedge  fence  and  a  road.  That  this 


1908]  .   THE  CoRN-Fn-xn  ANT  43 

field  had  been  heavily  infested  by  root-lice  the  preceding  year  was 
shown  by  the  number  of  aphis  eggs  and  young  aphids  in  possession  of 
the  ants — the  aphids  on  roots  of  smartweed  and  grasslike  weeds  in  the 
field.  The  ants  themselves  lived  mainly  under  ground,  at  least  by  day, 
rarely  opening  their  burrows  to  the  surface,  until  the  4th  of  May, 
when,  as  the  weather  warmed  up  after  a  heavy  rain,  they  made  their 
presence  known  by  a  deposit  of  pellets  of  earth  at  the  surface  around 
the  openings  of  their  burrows.  The  oats  at  this  time  were  about  four 
inches  high,  and  smartweeds  and  ragweeds  about  half  as  tall.  Both 
the  latter  had  many  root-lice  on  them,  but  none  were  on  the  roots  of 
the  oats,  and  the  aphis  eggs  were  not  yet  all  hatched.  Nests  of  the 
ants  were  very  abundant  in  the  grass  outside  the  borders  of  the  field, 
and  several  of  these  which  were  opened  up  contained  corn  root-aphids 
on  the  roots  of  the  grass.  From  the  8th  to  the  10th  of  May  the  ants 
were  actively  running  over  the  ground  as  if  in  search  of  food,  but,  so 
far  as  could  be  seen,  with  meager  result.  The  second  generation  of 
aphids  had  by  this  time  begun  to  appear,  and  many  of  the  smartweeds 
were  dead  at  the  root.  The  ground  was  very  dry  for  the  next  few 
days,  and  both  grain  and  weeds  grew  very  slowly,  many  of  the  oat 
plants  being  dead.  Thus  matters  went  on,  with  no  material  change 
except  that  the  ants  were  found  feeding  freely  on  dead  June-beetles 
and  other  insects,  until  June  5,  when  it  was  noticed  that  the  ants  were 
leaving  the  field. 

"As  I  was  returning  home  last  evening,"  says  Mr.  Kelly,  "I  no- 
ticed crossing  the  lane  beside  this  field  a  colony  of  Lasius  niger  ameri- 
canus,  composed  of  ants  going  in  both  directions  between  the  field  of 
oats  and  the  corn  field  on  the  opposite  side  of  the  road.  I  followed 
the  column  thru  a  hedge  fence  and  about  twenty  feet  into  the  oats, 
where  they  were  coming  out  of  their  nest.  Some  of  those  going  out- 
ward were  carrying  larvae,  but  none  of  those  returning  in  the  other 
direction.  The  line  of  march  was  indirect,  and  about  fifty-seven  feet 
long,  ending  in  the  grass  on  the  opposite  side  of  the  road,  where  a 
new  nest  was  being  formed.  The  colony  was  still  moving  at  6  the 
following  morning,  evidently  having  been  at  work  all  night.  They 
had  finished  the  transfer  before  8  a.  m.,  nothing  remaining  in  the  nest 
from  which  they  had  emerged.  No  root-lice  were  in  their  possession, 
but  only  their  own  larvae." 

Finally,  on  the  22d  of  June,  a  thoro  search  was  made  of  the  site* 
of  all  the  nests  marked  as  originally  occupied  by  ants.  Forty-nine  of 
the  fifty  were  identified,  the  remaining  one  being  lost.  Forty-four  of 
these  nests  had  been  completely  deserted,  and  only  five  were  still  in- 
habited by  ants.  '  These  were  in  rather  open  spots  in  the  field,  with  an 
abundance  of  grass  about  them.  There  were  no  corn  root-lice  on  this 
grass,  however,  but  only  the  grass  root-louse  (Schisoneura  panic  old) 
and  a  few  Geoica  squamosa.  The  oats  at  this  time  reached  about  to 
the  knee,  and  were  beginning  to  head. 

From  these  data,  combined  with  those  previously  published,  we 
may  infer  a  gradual  but  general  migration  of  the  ants  from  the  old 


44  BULLETIN  No.  131  [December, 

corn  field,  now  in  oats,  to  more  favorable  locations, — a  migration  which 
included  all  the  ants,  of  whatever  age  or  condition,  but  in  which  their 
aphid  possessions  were  apparently  sacrificed — probably  eaten  by  their 
owners  as  a  last  resort  of  domestic  economy.  Not  all  the  aphids  of 
the  oats  field  were  thus  lost,  however,  but  some  seem  to  have  been 
transplanted  to  grasses  near  by,  and  others,  which  acquired  wings  as 
food  began  to  fail,  escaped  by  flight,  Such  winged  aphids  were  re- 
peatedly seen  to  be  captured  by  wandering  ants,  who  took  them  in 
charge  and  placed  them  on  the  roots  of  suitable  plants.  Others,  light- 
ing by  chance  on  a  corn  plant,  made  their  own  way  down  the  stalk,  and 
thus  found  a  lodgment  on  the  roots,  where  they  were  doubtless  after- 
wards found  and  cared  for  by  ants.  Nevertheless,  the  loss  of  root- 
lice  consequent  upon  a  change  of  crop,  altho  not  complete,  must  have 
been  enormous,  only  now  and  then  one  of  the  aphis  inhabitants  of  the 
field  being  fortunate  enough  to  fall  upon  favorable  conditions;  and 
crop  rotation  remains  one  of  the  most  effective  means  of  checking  the 
multiplication  of  these  destructive  insects. 


1908] 


THE  CORN- FIELD  ANT 


45 


PLATE   I. 

STAGES  OF  THE  CORN-FIELD  ANT  (Lasius  niger  americanus)  :  worker;  larva; 
winged  male ;  pupa ;  winged  female ;  female  with  wings  removed. 


BF»  J  SP?  l/a%  JrP>4»L/J»  F>«^HBI 


